Lateral Seismic Anisotropy Variations Record Interaction Between Tibetan Mantle Flow and Plume‐Strengthened Yangtze Craton

Abstract

AbstractThe southeastern Tibetan Plateau experienced intense Cenozoic shortening and extrusion along the western Yangtze Craton, SW China, where the Permian Emeishan flood basalts were emplaced. Seismic anisotropy along a dense E–W‐trending linear seismic array across the west Yunnan is determined by shear‐wave splitting analysis to characterize the deformation associated with these processes. Interestingly, a strong N–S‐oriented anisotropic zone collocated with the Eocene–Oligocene potassic magmatism is observed between two weak anisotropic zones in the Three‐River Orogenic Zone and the western Yangtze Craton, respectively. The lateral anisotropy variation and distinct upper mantle structures collectively suggest that the western most Yangtze Craton, strengthened by the Permian mantle plume, acted as a rigid barrier to divert the Cenozoic Tibetan mantle flow into the Three‐River Orogenic Zone. Consequently, the western edge of the Yangtze Craton has been partially eroded and its anisotropic orientation was realigned to the direction of the mantle flow. This observation indicates that both the remodeled anisotropy in the lithosphere and the dynamic flow in the asthenosphere contribute to the mantle anisotropy at the lateral lithosphere‐asthenosphere transition, which is usually hard to seismologically resolve from the vertical lithosphere‐asthenosphere boundary.